ITER (the Latin word for "The Way") is a large-scale scientific experiment intended to prove the viability of fusion as an energy source. ITER is currently under construction in the south of France. In an unprecedented international effort, seven partners—China, the European Union, India, Japan, Korea, Russia and the United States—have pooled their financial and scientific resources to build the biggest fusion reactor in history. ITER will not produce electricity, but it will resolve critical scientific and technical issues in order to take fusion to the point where industrial applications can be designed. By producing 500 MW of fusion power from 50 MW of power injected in the systems that heat the plasma—a "gain factor" of 10—ITER will open the way to the next step: a demonstration fusion power plant.

On-site construction of the scientific facility began in 2010. As the buildings rise at the ITER site in southern France, the fabrication of large-scale mockups and components is underway in the factories of the seven ITER Members. The shipment of the first completed components began in 2014 and will continue into the 2020s. Machine assembly will begin as soon as the giant Tokamak Complex is ready for occupation. First Plasma is planned for December 2025.

ITER is one of the most complex scientific and engineering projects in the world today. The complexity of the ITER design has already pushed a whole range of leading-edge technologies to new levels of performance. However, further science and technology are needed to bridge the gap to commercialization of fusion energy.

What questions will be answered by ITER that have not already been answered by research to date?

ITER is the experimental step between today's fusion machines, focused on plasma physics studies, and tomorrow's fusion power plants.

The plasma physics community will have access, in ITER, to a one-of-a-kind device capable of plasma pulses of a much longer duration than those achieved in other fusion machines. ITER will be twice as large as the largest tokamak fusion experiment currently operating (JET in the UK), with ten times the plasma volume. This unique experimental machine has been designed to:

• produce 500 MW of fusion power (Q≥10) from 50 MW of heating input power• confine a deuterium-tritium plasma in which alpha-particle heating dominates• demonstrate the integrated operation of technologies for a fusion power plant• test components required for a fusion power plant• test concepts for a tritium breeding module

• demonstrate the safety characteristics of a fusion device

Today, fusion research is at the threshold of exploring a "burning plasma," in which sufficient heat from the fusion reaction is retained within the plasma and sustains the reaction for a long duration. Such exploration is a necessary step toward the realization of a fusion energy source. Scientists are confident that the larger ITER plasmas will not only produce much more fusion power, but will remain stable for long periods of time. The scale of ITER is necessary to break new ground in fusion science.

Is there consensus in the scientific community about the ITER Project?

In a project of this unprecedented scale, involving worldwide cooperation and billions of euros of expenditure, it would be naïve to believe that there could be unanimity in the scientific community on the aims and the scientific and technical basis of the project. A scientific consensus may be possible while discussions remain at the abstract level, but in a world of intense competition for research funding it is inevitable that scientists from various fields will criticize the decision to spend money on a large project, arguing that they would prefer to spend the money elsewhere.

What can be said about ITER is that for the scientific community working in the energy field, this project is considered by a strong majority as a major step that may provide a future energy alternative for all humankind. The present political and scientific approach to this project has not suddenly appeared out of lobbying by a few influential individuals. It is the result of decades of painstaking, step-by-step research by fusion scientists all over the world as well as intense discussions in the scientific administrations of involved governments who debated the options, the costs and the risks before deciding that ITER was a worthwhile investment in our common energy future. The proportion of papers directly concerned with ITER presented at leading international scientific conferences on fusion as well as in fusion journals has been steadily increasing for a number of years. The fact that research aimed at ITER is now such a dominant topic in these papers demonstrates how essential the project is to the advancement of fusion towards energy production.

Fusion research, and the role of ITER, has been subject to serious scrutiny by panels of independent experts established by funding agencies in Europe and most of the other ITER partners. The results of these investigations provide the most reliable measure of consensus in the scientific community. A few examples:

• In 2004 during the early stages of ITER negotiations, a high-level panel chaired by Sir David King (Chief Scientific Advisor to the UK government) concluded that the time was right to press ahead with ITER and recommended funding a "fast track" approach to fusion energy. In 2013 the European Fusion Development Agreement (EFDA) published a roadmap to the realization of fusion energy by 2050.

• The French Academy of Sciences organized a detailed review of the state-of-the-art and the remaining challenges of fusion both by magnetic confinement (including ITER) and using laser-driven systems. The review was published in a book in 2007 which emphasised the arguments supporting the construction of ITER.

• The United States went through a long process to decide to re-enter the ITER collaboration, after leaving it in the late 1990s. The US National Academy of Sciences convened a panel which included both fusion scientists and senior scientists from related fields such as nuclear fission power, high-energy physics and astrophysics. The non-fusion scientists were empowered to make the key recommendations. The panel strongly endorsed the renewed membership of the US in the ITER Project as the best path forward to fusion energy.

• China announced in 2011 that it is planning to train 2,000 skilled experts over 10 years to carry out research and development in fusion.

• In 2016, the US Department of Energy made a report to the US Congress in which it recommends that the US remain a partner in ITER, through a re-assessment in 2018. Noting that "the management of the ITER Organization and the performance of the project have improved substantially," the report concludes that despite accumulated delays, "ITER remains the fastest path for the study of burning plasma."

• In December 2017, the US National Academy of Sciences issued the first part of a two-phase study on the state and potential of magnetic fusion research in the US. In it, US policy makers were urged to continue to participate in the ITER Project and to develop a long-term strategy for fusion energy demonstration. (The report is available here.)

The first small-size tokamaks (1950s-1970s) were basic devices without sophisticated control systems and technology, but they demonstrated that high temperature plasmas could be generated and that energy could be confined. New plasma phenomena such as anomalous transport, instabilities and disruptions were uncovered during these first experiments. Scaling laws indicated that energy confinement could be increased in larger devices with higher magnetic fields.

The second-generation, medium-sized devices in the 1980s introduced the extensive use of auxiliary heating techniques. The addition of the divertor demonstrated improved confinement; wall conditioning techniques were also introduced. The ASDEX Tokamak achieved high confinement mode for the first time in 1982.

A new generation of larger tokamaks—JET (Europe), JT-60 (Japan), TFTR (US) and T-15 (Soviet Union)—were built to study plasmas in conditions as close as possible to those of a fusion reactor, and regularly upgraded based on advances in fusion science. New features such as superconducting coils, deuterium-tritium operation, and remote handling were introduced. The experience accumulated on these machines contributed to the design of ITER.

Today, fusion research is at the threshold of exploration of a "burning plasma" in which sufficient heat from the fusion reaction is retained within the plasma and sustains the reaction for a long duration. Such exploration is a necessary step toward the realization of a fusion energy source; it must be done to establish the confidence in proceeding with demonstrations of practical fusion energy. Construction of ITER and implementation of the ITER research program would provide for such exploration.

What are the advantages of ITER compared to the alternative approaches under development such as the W7-X Stellarator in Germany, and the inertial fusion programs in the US and France?

Of the magnetic confinement concepts for fusion (mainly tokamaks and stellarators) the main advantage of ITER and its tokamak technology is that, for the time being, the tokamak concept is by far the most advanced along the road to producing fusion energy. It is consequently pragmatism that dictated the choice of the tokamak concept for ITER. Stellarators are inherently more complex than tokamaks (for example, optimized designs were not possible before the advent of supercomputers) but they may have advantages in reliability of operation. The W7-X Stellarator, which celebrated its first plasma in 2015 in Greifswald, Germany, will allow good benchmarking against the performance of comparable tokamaks. These results will be incorporated in decisions about how DEMO, the next-generation fusion device after ITER, will look.

The inertial fusion concepts are something quite different. These technologies have mainly been developed to simulate nuclear explosions and were not originally planned to produce fusion energy. The inertial fusion concept has not demonstrated so far that it offers a better or shorter path than magnetic confinement to energy production. In Europe, the Euratom Framework Programs do not fund research on inertial fusion, but the program maintains a "watching brief" on developments.

The choice was made from the beginning to share the manufacturing of the most strategically important components among the seven ITER Members. This has considerably added to the complexity of the project, but the reasons for this decision were clear—by participating in ITER, each Member is preparing its industrial infrastructure, its scientific base, and its physicists and engineers for the next step on the road to fusion power: the construction of a demonstration fusion power plant.

It seems clear that no one Member has the financial and technical resources to build ITER alone. In this sense, by contributing only a portion of the project's costs, each Member benefits from the totality of the development program (where, already, there have been discoveries in technology, materials, science and even the first applications for patents) and, later, the totality of the 20-year experimental program.

Collaboration and coordination between the different entities of the project are improving all of the time. What is remarkable about fusion research is that, for a very long time, it has been an international, collaborative venture where discoveries in one area of the world immediately benefit other research programs. This is true every day at ITER, where the project benefits from the diverse experiences of its Members, including research underway on operational tokamaks in different parts of the world.

If ITER were only a construction project, its model would certainly have been organized differently. But as the world's largest and most challenging energy research project, the collaboration between seven ITER Members—all with decades of experience in fusion—has been most profitable in terms of pooling resources to solve the difficult challenges that remain on the road to fusion.

ITER is under construction now in Saint Paul-lez-Durance, southern France. Once the most important buildings are ready for occupation, the assembly of the machine and plant will begin. First-phase assembly, which will end with First Plasma, will be closely followed other assembly phases during which the in-vessel components (blanket, divertor, in-vessel coils ...) will be installed and the entire facility prepared for Deuterium-Tritium Operation.

Under the new Director-General Bernard Bigot, the ITER Organization and the Domestic Agencies conducted an eight-month, project-wide internal assessment in 2015 that scrutinized every detail of the ITER components and systems (from design, through manufacturing, delivery and assembly). The result—the best technically achievable project schedule and associated resource estimates—was presented to the ITER Council in November 2015 and subsequently reviewed by an independent group of Council-appointed experts.

In June 2016, the ITER Council endorsed the updated Resource-Loaded Integrated Schedule, through First Plasma; at its next meeting, in November 2016, it adopted the updated schedule through the start of Deuterium-Tritium Operation in 2035.

First Plasma is schedule for December 2025. This will be the official start of ITER operation. Please see our Project Milestones section for incremental milestones on the way to First Plasma.

When will the first giant ITER components travel along the ITER Itinerary?

The first Highly Exceptional Load (or HEL) travelled along the ITER Itinerary in January 2015.

The roads, bridges and roundabouts of the Itinerary were modified by France to meet the needs of the exceptional convoys that will transport ITER components arriving by sea to the ITER site.

Between 2015 and 2021 (estimated), 250 exceptional convoys will travel along the ITER Itinerary with their extra-large cargo by night, at reduced speeds. The heaviest? 900 tonnes. The tallest? 10 metres. The widest? 9 metres. The longest? 33 metres. We're expecting each one of these exceptional convoys to be quite a local event.

For a first-of-a-kind project like ITER, challenges to the schedule along the way can be expected. It certainly took longer to build up the ITER Organization—and establish world-class systems for managing the project—than was originally foreseen.

A 2013 Management Assessment of the project identified a number of other root causes: a complex, multinational structure; inefficiencies related to the sharing of work among many parties; underestimated staffing needs; and lack of strong central management.

Because the ITER Organization and the Domestic Agencies all have equal stakes in completing the ITER Project, strong measures have been set into place to track schedule performance. For critical areas, specific recovery actions have been set into motion, for example measures to reduce delays in the signature of agreements and contracts, accelerate and optimize design review and design change processes, strengthen central engineering and configuration control, and improve collaboration in schedule-critical areas (vacuum vessel manufacturing, building construction ...).

A project-wide schedule updating exercise in 2015 has resulted in a new calendar for ITER that has been approved by the ITER Council through First Plasma (schedule for December 2025) and Deuterium-Tritium Operation (scheduled to begin in 2035). Against this new calendar, the project is on track.

Progress is monitored and reported to the ITER Council on the basis of high-level milestones. For the years 2016 and 2017, the ITER Organization and the Domestic Agencies have met every agreed milestone. In November 2017, the "50 percent mark to First Plasma" was passed, meaning that of all sequential activities on the path to beginning ITER operation (from component and plant design activities through component manufacturing, building construction, shipping and delivery, assembly, installation and commissioning) 50 percent have been achieved.

A strengthened risk and opportunity management approach, in which risks to the schedule are identified, prioritized, and mitigated, allows increased confidence in the achievement of the schedule.

What are the Members doing to address the project's difficulties/schedule delays?

In March 2015, a new ITER Director-General, Bernard Bigot (from France) took over at the helm of the project. He is currently implementing a project-wide action plan that has received the support of all Members.

The ITER Project is entering a critical phase, as Tokamak Complex construction is underway and the fabrication of strategic ITER components (magnets, vacuum vessel, cryostat ...) has been launched. A new organization—centred on deliverables and strong project management—is being set up within the ITER Organization Central Team, and a new way of working in an integrated way with the ITER Domestic Agencies has been established.

A closer working relationship among the Members and between the Members and the ITER Organization Central Team will allow faster and more informed decision making and issue resolution. A new Executive Project Board associates the management of the ITER Organization Central Team and that of the Domestic Agencies.

Through close collaboration and close tracking of the schedule, solutions are being sought to improve manufacturing performance for the systems and components required for the first experiments. Close collaboration with industry, for example, has already resulted in the recovery of some delay.

Quality control is also essential—we have to make sure all the components will fit and work together. Within the ITER Organization, there is a team dedicated to quality assurance (QA) and quality control (QC). Its members help oversee and ensure that the proper QA/QC practices are implemented at companies manufacturing the reactor's components.

We hear the project is delayed. Are the ITER Members prepared to contribute additional budget?

The updated schedule for the ITER Project identifies December 2025 as the "best technically achievable" date for First Plasma. Endorsed by the ITER Council in June 2016, the updated schedule comes with a revised estimate of the overall cost of the project, including increased staff resources.

In November 2016, the ITER Council approved the complete updated project schedule through Deuterium-Tritium Operation in 2035. The ITER Members will now go through their domestic processes of obtaining approval for the associated overall project cost.

The ITER partners are taking a number of actions to ensure that they have control over the cost of the project:

By focusing now on the achievement of First Plasma, financial and human resources are concentrated in the near-term on core industrial elements and overall project risk is lowered.

By implementing a staged approach (First Plasma followed by a number of progressive phases to equip the machine for Deuterium-Tritium Operation interspersed with operational phases), confidence is increased and risk is minimized.

By closely monitoring project risks and opportunities, and tracking against agreed milestones, any potential deviation from optimum progress can be identified at an early stage and mitigated.

By freezing the design of all interfacing First Plasma components, the risk of delay due to project change requests is averted.

The ITER Council is also considering a proposal for regular reviews in order to validate the project's step-by-step progress and also to have the benefit of expert independent counsel in implementing best-practice.

Was the ITER Project schedule affected by the natural disaster in 2011 in Japan?

The earthquake and tsunami in Japan on 11 March 2011 affected some of the installations producing components for ITER. In particular, the buildings for superconducting magnet test equipment and neutral beam test equipment were seriously damaged.

The ITER Organization did everything possible within the scope of its mandate to minimize the impact of the Japanese disaster on the ITER Project schedule. With effort and ingenuity, and strong support from the ITER Domestic Agencies, the delay in First Plasma was contained to one year.

Is there any danger that ITER will experience start-up difficulties as, for example, the LHC had with its array of magnets?

Once integrated and assembled, the ITER machine will go through a period of testing and commissioning. This is the equivalent of making sure that "all systems are go" before attempting the first experiment. Next, a several-year "shakedown" period of operation in pure non-nuclear fuels such as hydrogen, helium and deuterium is planned during which the machine will remain accessible for repairs and the most promising physics regimes will be tested. This phase will be followed by operation in deuterium with a small amount of tritium to test wall-shielding provisions. Only then, scientists will launch a third phase with increasingly frequent operation with an equal mixture of deuterium and tritium, at full fusion power.

The ITER superconductors have been the object of a particularly stringent development and qualification program. Conductor samples from every supplier undergo testing at the SULTAN installation, located at the Paul Scherrer Institute (PSI) in Villigen, Switzerland, before acceptance by the ITER Organization. At SULTAN, the samples are exposed to magnetic fields, current intensity and temperature conditions that are equivalent to those of the ITER operational environment.

In addition, for the 18 D-shaped toroidal field coils, the ITER Council has requested that a common set of specifications be developed for the cold testing at 77 K (minus 196 °C) of the first three coils in each series of toroidal field winding packs as a risk mitigation measure.

During the construction phase of the project, Europe has responsibility for approximately 45.5 percent of construction costs, whereas China, India, Japan, Korea, the Russian Federation and the United States will contribute approximately 9.1 percent each. The lion's share (90 percent) of contributions will be delivered "in-kind." That means that in the place of cash, the Members will deliver components and buildings directly to the ITER Organization.

The in-kind contributions of the ITER Members have been divided into approximately 140 Procurement Arrangements. These documents detail the technical specifications and management requirements for the procurement of plant systems, components or site construction. The value of each Procurement Arrangement is expressed in ITER Units of Account (IUAs), a currency devised to measure the value of in-kind contributions to ITER consistently over time.

Procurement allocations were assigned among the Members on the basis of valuations of components. Upon successful completion of a component, the corresponding credit value is credited to the Members' account. Contributing 9.1 percent of the project, therefore, becomes a matter of adding up the IUA value of the different contributions.

For the operation phase, the sharing of cost amongst the Members will be as follows: Europe 34 percent, Japan and the United States 13 percent, and China, India, Korea, and Russia 10 percent.

France contributes to the ITER Project as a member of the European Union. The country's commitment to ITER "at the level of EUR 1.2 billion through to 2017" was confirmed by French Minister of Research and Higher Education Geneviève Fioraso on the occasion of the ITER Headquarters inauguration (17 January 2013). Furthermore, France has contributed a number of in-kind contributions for a total of approximately EUR 260 million (ITER site preparation, the International School in Manosque and the realization of the heavy haul Itinerary). The French financial and in-kind contributions originate from the French government as well as from the local governments of the Provence-Alpes-Côte d'Azur region where ITER is located, who have pledged a total of EUR 467 million to the ITER Project over a period of 10 years.

This contribution is on par with the contracts and employment that have already been generated in the area by the ITER Project. (See section on Economic Benefits.)

For all Members, the potential benefits of participation are significant: by contributing a portion of the project's costs, Members benefit from 100 percent of the scientific results.

Based on the 2001 design, the original cost estimate of ITER was EUR 5 billion for construction costs. This estimate, based on the best available information at the time, did not include some labour costs, escalation and contingency. It also did not properly estimate the time needed for the assembly and commissioning phases of the first-of-a-kind ITER Tokamak, or include some later-term matters such as component storage.

In 2008, a detailed design review called for modifications to the ITER machine based on advancements in fusion science; these modifications, such as the addition of vertical stability and Edge Localization Mode (ELM) coils, were incorporated into the 2010 Baseline and added to overall cost. The fact that the number of ITER Members passed from four to seven also contributed to cost increases by creating a much larger number of interfaces (and hence, complexity) within the design. The third important element of the cost increase is that building construction costs have increased significantly since the 2001 estimate. Raw material costs have doubled (steel) or tripled (concrete).

In 2015, the ITER Organization conducted an in-depth review and analysis of all aspects of manufacturing and assembly of the ITER systems, structures and components. The resulting updated schedule and overall cost estimate reflect a more advanced level of design maturity and a much-improved understanding of the scope, sequencing, risks, and costs of the ITER Project. The schedule exercise identifies December 2025 as the best technically achievable date for First Plasma and 2035 as the start of Deuterium-Tritium Operation. Both dates are contingent on resources.

With the new updated project schedule, the ITER Members now have all the elements needed to go through their domestic processes of obtaining approval for associated resources.

Because multiple Members are collaborating to build ITER, each with responsibility for the procurement of in-kind hardware in its own territory with its own currency, a direct conversion of the value estimate for ITER construction into a single currency is not relevant.

Prior to the 2016 budget updating exercise, the European Union had estimated its global contribution to the costs of ITER construction at EUR 6.6 billion, with other Domestic Agency contributions depending on the cost of industrial fabrication in those Member states, which can be higher or lower, and their percentage contribution to the construction of ITER. Based on the European evaluation, the cost of ITER construction for the seven Members had been evaluated in the past at approximately EUR 13 billion (if all the manufacturing was done in Europe).

At the ITER Council meeting in November 2016, the ITER Organization proposed a complete updated project schedule through First Plasma (2025) and on to Deuterium-Tritium Operation (2035). The overall project cost in line with the revised schedule was approved ad referendum, meaning that it will now fall to each Member to seek approval of project cost through respective governmental budget processes. The costs associated with the resources estimated in the Updated Long-Term Schedule would add EUR 4 billion to the original estimate.

ITER is financed by seven Members: China, the European Union (plus Switzerland, as a member of EURATOM), India, Japan, Korea, Russia and the United States. In all, 35 countries are sharing the cost of the ITER Project.

For the other phases of the ITER Project the cost estimates have not changed. Operation of the ITER installation during its experimental lifetime (approximately 20 years) is estimated at 188 kIUA* per year. For the Deactivation (2037-2042) and Decommissioning phases, the costs have been established in euros at EUR 281 million and EUR 530 million respectively (EUR in 2001 values).

*The ITER Unit of Account was created as part of the ITER Agreement to equitably allocate the value of in-kind hardware procurement to each Member. In 2016, 1 IUA = EUR 1,690.12.

Is it worth spending billions on fusion or would the money be better spent in improving renewables like solar, wind and geothermal?

In a global context of rising oil and gas prices, decreased accessibility to low-cost fossil fuel sources, and an estimated three-fold increase in world energy demand by the end of this century, the energy question finds itself propelled to centre stage. How will it be possible to supply this new energy without adding to greenhouse gases?

Investing in renewables such as solar, wind and geothermal is important. Just like in fusion R&D ... with significant investment comes advancements in technology, and with advancements in technology comes a decrease in price. All calculations point to an increase in the importance of renewables in the decades to come.

The ideal future energy mix would hold a mixture of generation methods instead of a large reliance on one source. Fusion offers advantages that make it worth pursuing: widely abundant, inexpensive and virtually unlimited fuels, and the ability to operate in a base load capacity, which is not easy for generation methods based on intermittent sources, such as wind or sun.

The fusion community doesn't see itself in competition with renewable forms of energy. Rather, in a world ever more dependent on energy, it is important to follow all of the promising options for our common future.

The ITER Organization manages its cost estimate and associated risk in the same way as any large project, using industry-standard software and risk analysis. There is always a risk for a construction project managed over several years that certain "external" factors (labour, building materials) or "internal" factors (the complexity of increased interfaces in the design, design changes, nuclear safety authority requirements or inspections, etc.) have an impact on the budget.

To track the risk of cost increase, each activity in the ITER Organization cost estimate is assigned a level of uncertainty in accordance with a risk classification system. The values of the activities and their uncertainty classifications are then analyzed to predict confidence levels. These important tools allow management to identify and react to possible cost increases.

To compensate for the risk associated with the uncertainty in the cost estimate, the ITER Organization at all times seeks cost savings to be able to offset potential cost increases.

Has ITER resulted in any positive economic benefits locally? Is ITER creating jobs?

ITER is creating jobs, and not only locally.

First, consider the R&D and fabrication activities that are going on for ITER around the world. In 2016, the ITER Domestic Agencies estimated the number of contracts awarded related to the development and procurement of ITER systems, components and infrastructure at over 3,000—the direct beneficiaries of these contracts are the laboratories, universities and industries in ITER Member countries. (Contracts are also awarded directly by the ITER Organization.) These contracts—many of which demand skilled contributions in engineering—are significantly more labour-intensive than conventional industrial manufacturing. An estimated EUR 3 billion are engaged in ITER manufacturing around the world.

It is estimated that over three-fourths of the total European construction contribution to ITER will be directed to industry, a proportion that is similar in other Members.

Since 2007, 1,200 people have worked on the preparation of the ITER site, the construction of the Provence-Alpes-Côte d'Azur International School, and the ITER Itinerary. A further 2,500 people have been involved in ITER construction (for the period mid-2010 to 2014). Today, approximately 3,000 people work for the ITER Project in Saint Paul-lez-Durance (ITER staff, contractors, temporary agents, European Domestic Agency staff and subcontractors); these employees contribute, with their families, to the economic life of the region.

During the peak of construction and assembly works (2017-2019), 3,000-4,000 workers will be employed on the ITER site.

Contracts totalling EUR 5.48 billion have been attributed since 2007 by the ITER Organization, the European Domestic Agency for ITER (responsible for the in-kind contribution of Europe to ITER, including all buildings), and Agence Iter France. Within this total, French companies have been awarded EUR 3.06 billion worth of contracts, of which 72% (worth EUR 2.21 million) were attributed to companies based in the PACA region (statistics for the period ending 31 August 2017).

Q—also called "fusion gain"—measures the ratio between the power produced by the fusion reactions, and the external heating power that must be injected in a tokamak to sustain the reactions.

Let's review how ITER will create the conditions for fusion inside its vacuum chamber.

Fuel is injected in gaseous form into the vacuum vessel (the gas weighs only a few grams and fills the entire volume of the tokamak);

Electricity flowing through the electromagnets, particularly the central solenoid, produces a voltage across the gas;

This voltage rips electrons from the fuel atoms, turning them into charged particles (ions). This new state of matter is called a plasma;

The changing magnetic fields that are used to control the plasma produce a heating effect (read about "ohmic heating" here). But in order to obtain the temperatures approaching 150,000,000 °C that are needed for deuterium-tritium fusion, three sources of external heating must be applied from outside of the tokamak;

The megawatts of heating power injected by these external systems is part of the ratio measured by Q, which compares input heating power to output fusion power.

In ITER, the programmatic goal, Q≥10, signifies delivering ten times more power (500 MW) than that which is delivered by the heating systems (50 MW).

Very. Breakeven, which corresponds to Q=1, is the moment when the total fusion power produced during a plasma pulse equals the power injected into the systems that heat the plasma. This has never been achieved in a fusion device; the current record worldwide is held by the European tokamak JET (UK), which succeeded in generating a Q of 0.67 in the 1990s. ITER is the machine that has been designed to do it, which explains the participation of so many nations—who run domestic fusion programs at home—in the international collaboration surrounding the project.

ITER's Q value of ≥10 makes it a first-of-kind machine and a unique scientific device.

The fusion between the nuclei of the hydrogen isotopes deuterium (D) and tritium (T) produces one helium nucleus, also called an "alpha particle," and one neutron.

The helium nucleus, which carries 20 percent of the energy produced by the fusion reaction, is electrically charged and remains confined by the magnetic fields of the tokamak (whereas the neutron escapes). The heating provided by these alpha particles contributes to maintaining the temperature of the plasma and decreases the need for external heating. When heating by the helium nuclei ("alpha heating") is dominant (over 50 percent) the plasma is said to be a "burning plasma."

This is a state of matter that has never been produced in a controlled manner on Earth.

Yes, it will, and there is a large worldwide consensus around the necessity of building such a device. Achieving a burning plasma in which at least 50 percent of the energy to drive the fusion reaction is generated internally through the alpha particles is an essential last step in the 70-year quest to control fusion reactions in a magnetic fusion device.

At Q = 5, approximately 50 percent of the plasma heating is contributed by the alpha particles. At Q = 10 (ITER), this percentage rises to 66 percent. At Q=20 alpha heating represents 80 percent.

The primary motivation behind the design of ITER is to provide Members scientists with the opportunity to study, and better understand, a burning plasma. The knowledge acquired in ITER will help scientists and engineers design the commercial fusion-generated electricity plants of the future. As a research device, ITER will be equipped with far more diagnostics and other research components than the commercial facilities that will follow.

Accounting for the size of ITER's vacuum vessel and the strength of the confining magnetic field (5.3 Tesla), the ITER plasma (830 cubic metres) can carry a current of up to 15 megaamperes.

Under these conditions, an input thermal power of 50 megawatts is needed to bring the hydrogen plasma in the vessel to about 150 million degrees Celsius. This temperature in turn translates to a high enough velocity, among a sufficient population of hydrogen nuclei, to induce fusion at a rate that will produce at least 500 megawatts of thermal power output.

Why not design ITER for a Q of 30, or 50? The answer is clear: expense. For tokamaks, size matters: if all other parameters are equal, larger size means greater Q. In simple terms, increasing Q would require an increase in the major radius or in the magnetic field strength. Either approach would have increased the cost of the device unnecessarily, whereas the achievement of Q ≥ 10 is sufficient to allow the primary scientific and technology goals of the project to be satisfied.

This would also have required an increase in cost with no great benefit to the goals of the project. ITER is an experimental device designed to operate with a wide range of plasma conditions in order to develop a deeper understanding of the physics of burning plasmas, and to allow the exploration of optimum parameters for plasma operation in a power plant. The addition of the systems required to convert fusion power to high temperature steam to drive an electricity generator would not have been cost-effective, since the pattern of experimental operation of a tokamak such as ITER will allow for very limited generation of electricity.

What is the difference between plasma energy breakeven and engineering breakeven?

Plasma energy breakeven is the moment when the efficiency of the fusion reaction reaches Q = 1 (please see explanations on "Q" in the preceding paragraphs); that is, when the total fusion power produced during a plasma pulse equals the power injected into the systems that heat the plasma. This important scientific goal—never before achieved—is the "raison d'être" for the scale of ITER and the design of many of its key technological systems (superconducting magnets, external heating, blanket, divertor, etc.).

Engineering breakeven would take into consideration all of the plants systems—and not just external heating systems—in the evaluation of the input/output power balance of an electricity-producing fusion power plant. Commercial fusion plants will be designed based on a power balance that accounts for the entire facility: the electricity output, sent to the industrial grid, compared to the electricity consumed by the facility itself—not only in tokamak heating, but also in secondary systems such as the electricity used to power the electromagnets, cool the cryogenics plant, and run diagnostics and control systems.

Some say that ITER construction will rely on migrant workers who are poorly paid and precariously housed. Is this true?

No, it's not. The workers on the ITER construction site are protected by French law, which provides that all companies operating in France, whatever their "nationality," are subjected to French labour regulations and more specifically the regulatory minimum salary.

In addition, in accordance with the ITER Agreement the ITER Organization observes applicable French laws and regulations concerning public and occupational health and safety (see the next question for more information on the ITER Organization's legal status). On-site inspections by the competent authorities are regularly performed on the ITER worksite, just as they are for all large construction projects in France.

Concerning the housing of workers who do not live locally, the construction companies operating on the ITER site have a contractual obligation to provide it. The quality of all housing solutions must strictly comply with French regulations.

Like the United Nations, UNESCO, the World Health Organization, the International Monetary Fund, CERN, or Interpol for example, the ITER Organization is an international organization created by international treaty (the ITER Agreement was signed by the seven ITER Members on 21 November 2006 in Paris). As such, it benefits from a specific legal status recognized by international law that confers certain rights to the ITER Organization; for example, the inviolability of its site, its goods, and its official documents.

In certain domains, the ITER Organization must observe French laws and regulations. Article 14 of the ITER Agreement provides that the ITER Organization shall observe the applicable laws and regulations of the Host state (France) in the following fields:

public and occupational health and safety;

nuclear safety;

radiation protection;

licensing;

nuclear substances;

environmental protection;

protection from acts of malevolence

The Headquarters Agreement signed between France and the ITER Organization on 7 November 2007 further provides that the Director-General of the ITER Organization shall cooperate with French authorities to establish framework programs of inspections and controls in accordance with French laws and regulations to be observed in the domains listed above.

In parallel, French law applies to companies involved in ITER construction and to their employees. At this level, there is no difference between the ITER Project and any other construction project in France.

As explained in the preceding questions, French law protects the on-site construction workers. Irrespective of the nationality of the company that has been awarded a building contract or the nationality of the workers, French labour regulations and collective agreements per branch ("conventions collectives") apply. In 2011, the French government drafted guidelines detailing the full set of obligations and responsibilities of a foreign construction company participating in the ITER Project including, for example, pay scales per branch and per level of qualification. The application of these rules is strictly controlled by the French authorities. All subcontractors working on the ITER site, whether for the ITER Organization or one of the Domestic Agencies, have a copy of these guidelines.

Staff employed directly by the ITER Organization (approximately 700 people from 30 nationalities) is hired under the specific regime of an international organization and benefits from the status of international civil servant. Other employees (contractors, temporary agents ...) who work in the office buildings fall under the regime of French work codes and regulations.

​As Host Member to the ITER Project, Europe has the responsibility to build nearly all of the 39 buildings and technical areas of the ITER platform. The Domestic Agency for Europe (Fusion for Energy) is thus charged with managing the tender offers for the building projects entrusted to Europe and awarding the related contracts (principally to European companies).

Fusion for Energy has put into place a rigorous qualification process for companies. Companies must prove:

conformity with laws and regulations and contractual requirements at an administrative level (up-to-date insurance policies and social contributions);

conformity with laws and regulations and contractual requirements in terms of security (companies must submit valid security and occupational health policies);

technical conformity (the contractor must prove that it has the technical capacity to carry out the work demanded).

Meeting these conditions is a requirement for any company hoping to be awarded a construction contract with Fusion for Energy. Fusion for Energy can exercise its right of audit at any time during the execution of contractual works.

According to the European Domestic Agency construction contracts, a maximum of two tiers of subcontracting is permitted. Accordingly, no part of the contracted works may be subcontracted to a third tier unless otherwise approved by Fusion for Energy. Compliance with this clause is closely monitored and up to now this requirement has been complied with strictly.

How many workers are expected on the ITER worksite in the years to come? What percentage will come from outside of France?

The construction of the ITER facility is estimated at 18 million person hours. The number of workers is expected to reach a peak between 2020 and 2022, with close to 2,000 people involved with the construction activities.

In parallel, a large workforce will be required for the machine and plant assembly operations that will begin as each building is handed over from the Domestic Agencies to the ITER Organization. According to current estimations, the assembly workforce will reach a peak between 2021 and 2024 at about 1,800 workers. In 2021/2022, when the construction workforce begins to decrease and the assembly workforce begins to build up, the number of workers on the ITER work site will climb to nearly 4,000 people.

The majority of these workers are French. According to statistics provided by the European Domestic Agency, Fusion for Energy, from mid-2010 to mid-2014 ninety-five percent of the 2,500 people who worked on the ITER work site were European. The complete breakdown is as follows: French (69.2%), Spanish (11.9%), Portuguese (4.7 %), Romanian (3.8%), British (2.6%), Moroccan (1.6%), Algerian (1.5 %), Tunisian (0.9%), Italian (0.7%) and German (0.6%).

I've heard that foreign workers on the ITER site are only paid EUR 300 per month. Is this true?

Certainly not. As stated above, contractors and subcontractors on the ITER site must comply with French law. All workers on the ITER site are paid at least the French minimum wage. In case of infringement, the incriminated company would immediately be denied approval. For part time work, workers are paid a pro-rata percentage of the legal full-time wage, in accordance with the number of hours worked.

What controls are carried out by the French authorities on site working conditions?

The modalities of collaboration between the ITER Organization and the French labour inspectorate were defined in the Headquarters Agreement signed between the French government and the ITER Organization, as well as in an additional protocol relating to on-site labour inspections concerning occupational health and safety. The French labour inspectorate can carry out unplanned inspections, as foreseen in Article 3 of the Headquarters Agreement and in the annual program of inspections. The ITER Organization has provided the labour inspectorate with a permanent access badge.

In addition, on 1 February 2013 the ITER Organization signed a partnership arrangement with the French social security agency URSSAF PACA. By doing so, the ITER Organization has committed to facilitating that agency's mission of prevention—through information, education and inspection—of illegal labour practices on the ITER construction site. URSSAF PACA will organize information/training sessions on labour laws and regulations for all companies involved in ITER construction and inspections will be carried out on a regular basis.

The ITER Organization is working in full collaboration with URSSAF in line with the access rules applicable on the ITER site. The ITER Organization is informed in advance of planned URSSAF inspections to prepare the access but this does not mean that contractors are informed. It is in the interest of the ITER Organization and of the project as a whole that the French authorities implement the necessary on-site control of working conditions.

Several construction companies have reported the late payment of invoices. What is the situation?

European Domestic Agency construction contracts are based on FIDIC conditions—an international standards organization for the construction industry. Contractors are entitled to an advance payment in the range of 10% of the contract price. A schedule of payments is attached to the contract which specifies the further instalments to be paid to the contractor and the conditions for payment.

Each contractor submits its estimates monthly to the Engineer in charge of the management of the construction site. This estimate presents the detail of the amounts considered owed and supporting documents proving work progress. The Engineer certifies the amounts owed in relation to work performed and issues a payment certificate that is used by the contractor to submit its invoice to the European Domestic Agency (Fusion for Energy). The Engineer can withhold the payment certificate in a few cases only, each related to the breach of the contractor's specified obligations under the contract.

According to the terms of the contract, Fusion for Energy pays the stated amount after receipt of the contractor's invoice (usually within 45 days). In the event of delayed payment, the contractor is entitled to late payment interest. Furthermore, Fusion for Energy work contracts specify that the contractor shall be wholly responsible for paying any amounts properly due (and undisputed) to its subcontractors.

What are the plans for housing thousands of people involved with ITER construction and assembly works?

For workers who do not live locally, housing and transportation fall under the responsibility of the companies operating on the ITER site who have a contractual obligation to provide it.

Agence Iter France, local authorities and regional state services have been investigating various housing possibilities and projects within 30 minutes' drive from the ITER site. Companies are encouraged to contribute to projects under development. In 2015, several sets of offers are likely to become available. Of course, the quality of all housing solutions will strictly comply with French regulations. A housing guide for ITER workers was issued in June 2014 and will be updated as needed.

Will infrastructure modifications be necessary to absorb the increase in traffic flow around the ITER site?

To minimize the risk of congestion in the vicinity of both the CEA-Cadarache and ITER sites, the following measures will be important: strengthening the public transport network, carpooling, and staggering the arrival and departure times for ITER site workers. Infrastructure modifications are also under study.

It took several years to achieve the licensing of ITER as an "Installation Nucléaire de Base" under French law.

• The ITER Organization submitted a Preliminary Safety Report in March 2010 to the French Nuclear Safety Authority, which allowed the technical examination of the ITER safety files to begin;

• The French Environmental Authority, whose opinion on ITER's nuclear licensing files is required in accordance with the EEC Directive 97/11/EC of 3 March 1997 on Environmental Assessments, delivered its opinion on 23 March 2011. The opinion was favourable and included several recommendations to be taken into account by the ITER Organization;

• A Public Enquiry was held locally in the communes surrounding the ITER site from 15 June-4 August 2011. On 9 September 2011 the Public Enquiry Commission issued a favourable Advisory Opinion;

• The technical examination of the files by the Institute of Radioprotection and Nuclear Safety (IRSN), acting as the ASN's technical expert, began during the summer of 2010. In September 2011 the IRSN submitted a 300-page report—including 800 questions to the ITER Organization—to a group of 30 experts appointed by ASN, the Groupe Permanent. The Groupe Permanent issued a favourable report at the end of 2011;

• The ITER Organization was informed in writing by the French safety authorities (ASN) on 20 June 2012 that, following an in-depth technical inspection, the operational conditions and the design of ITER as described in the ITER safety files fulfilled expected safety requirements at this stage in the licensing process. Following this, the draft decree was communicated by the ASN to the French government for signature;

• On 10 November 2012, the French Prime Minister Jean-Marc Ayrault signed the official decree that authorizes the ITER Organization as an "Installation Nucléaire de Base."

ITER is the first nuclear installation in France to observe the stringent requirements of the 2006 French law on Nuclear Transparency and Security. It is also the first time in worldwide history that the safety characteristics of a fusion device have undergone the rigorous scrutiny of a Nuclear Regulator to obtain nuclear licensing. ITER has achieved an important landmark in fusion history.

Will the post-Fukushima nuclear safety stress tests apply to ITER? If so, is there any risk that these stress tests will lead to additional costs?

Following the natural disaster in Japan in March 2011, and the resulting tsunami and nuclear accident at Fukushima Daiichi, the French government requested the French Nuclear Safety Authority ASN to carry out complementary safety assessments. The decision was made to assess not just nuclear power plants, as requested at the European level, but also research infrastructures in order to examine the resistance of everyfacility in the face of a set of extreme situations leading to the sequential loss of lines of defence, such as very severe flooding, a severe earthquake beyond that postulated in the ITER safety case, or a combination of both.

The ITER Organization provided a nuclear safety stress report to the French safety authorities on 15 September 2012. The technical examination of the report was concluded in July 2013 by a standing session of the Groupe Permanent in France. This group of experts appointed by ASN communicated only one recommendation to the ITER Organization: to study extreme climatic conditions such as tornado, hailstorms, etc.

Taking into account the robustness of the ITER safety design, this stress test report should not lead to additional cost.

What kind of nuclear waste will be produced by ITER, and in what quantity?

Fusion reactors, unlike fission reactors, produce no high activity/long-lived radioactive waste. The "burnt" fuel in a fusion reactor is helium, an inert gas. Activation produced in the material surfaces by the fast neutrons will produce waste that is classified as very low, low, or medium activity waste. All waste materials will be treated, packaged, and stored on site. Because the half-life of most radioisotopes contained in this waste is lower than ten years, within 100 years the radioactivity of the materials will have diminished in such a significant way that the materials can be recycled for use (in other fusion plants, for example). This timetable of 100 years could possibly be reduced for future devices through the continued development of "low activation" materials, which is an important part of fusion research and development today.

The activation or contamination of in-vessel components, the vacuum vessel, the fuel circuit, the cooling system, the maintenance equipment, or buildings will produce an estimated 30,000 tonnes of decommissioning waste that will be removed from the ITER scientific facility and processed.

What arrangements are foreseen for radioactive waste generated by ITER during operation and decommissioning?

ITER, as operator, will bear the financial responsibility for the temporary and final storage of operational radioactive waste. Host State France will be in charge of the dismantling phase and the management of the waste resulting from this dismantling; the cost for these activities will be provisioned by ITER during the operation phase and shared by the Members. France will also be responsible for providing temporary storage for part of the operational waste, pending its final disposal; this will be financed through ITER operation cost.

What effect will ITER operation have on local electricity and water supplies?

Electrical supply to the ITER site will be assured by an existing network that feeds the Tore Supra Tokamak—part of the adjacent CEA Cadarache research facility. The French electricity provider RTE completed a 4-hectare switchyard on the ITER platform and the connection to the main network in June 2012. Operating the ITER Tokamak will require from 120 MW to up to 620 MW of electricity for peak periods of 30 seconds. No disruption to local users is expected.

Concerning water supply, approximately 3 million cubic metres of water will be necessary per year during the operational phase of ITER. This water will be supplied by the nearby Canal de Provence, and transported by gravity through underground tunnels to the fusion installation. The volume of water needed for ITER represents only 1 percent of the total water transported by the Canal de Provence. The combined effect of the ITER installation and the adjacent CEA facilities remains below 5 percent of the total volume of water transported by the Canal de Provence.

Is the energy stored in a 100-million-degree plasma dangerously large?

Although 100 million degrees Celsius is an extremely high temperature, the density of the plasma (atoms per cubic metre) is very low—about one million times less than air—and the total energy in the plasma is not very great. The very rapid release of the energy could cause superficial damage to some plasma-facing components (i.e., surface melting) but would not be sufficient to produce structural damage.

What would be the danger of an earthquake occurring near ITER, or a double disaster like earthquake and flooding?

The ITER facility is designed to resist an earthquake of amplitude x40 and energy x250 higher than any earthquake for which we have historical or geological references in the area of Saint Paul-lez-Durance, France. The ITER Tokamak Building will be made of specially reinforced concrete, and will rest upon bearing pads, or pillars, that are designed to withstand earthquakes (this technology is used to protect other civil engineering structures such as electrical power plants from the risk of earthquake). The risk of flooding, too, has been taken into account in ITER's design and Preliminary Safety Report. In the most extreme hypothetical situation—that of a cascade of dam failures north of the ITER site—more than 30 metres remains between the maximum height of the water and the first basemat of the nuclear buildings.

Following the natural disaster in Japan in March 2011, and the resulting tsunami and nuclear accident at Fukushima Daiichi, the French government requested that the French Nuclear Safety Authority (ASN) carry out complementary safety assessments. The decision was made to assess not only nuclear power plants, as requested at the European level, but also research infrastructures in order to examine the resistance of a facility in the face of a set of extreme situations leading to the sequential loss of lines of defence, such as very severe flooding, a severe earthquake beyond that postulated in the ITER safety case, or a combination of both.

The ITER Organization provided a nuclear safety stress report to the French safety authorities on 15 September 2012. The technical examination of the report was concluded in July 2013 by a standing session of the Groupe Permanent in France. This group of experts appointed by ASN communicated only one recommendation to the ITER Organization: to study extreme climatic conditions such as tornado, hailstorms, etc.

The ITER design takes into account external hazards in accordance with French regulation and practices. The Preliminary Safety Report submitted by the ITER Organization to the French licensing authorities includes an in-depth analysis of external hazards, including man-made hazards. This includes the consequences of events such as aircraft crashes, and part of the Preliminary Safety Report is dedicated to providing evidence of ITER safety even against malevolent acts.

In a tokamak fusion device, the quantity of fuel present in the vessel at any one time is sufficient for a few-seconds burn only. It is difficult to reach and maintain the precise conditions necessary for fusion; any disruption in these conditions and the plasma cools within seconds and the reaction stops, much in the same way that a gas burner is extinguished when the fuel tap is turned off. The fusion process is inherently safe; there is no danger of run-away reaction or explosion.

No! What happened in the fission reactors in northeastern Japan following the severe earthquake and subsequent tsunami in 2011 could not happen at ITER. This is due to the fundamentally different physics and technologies used in fission and fusion reactors.

In a fusion reactor, there will only be a very limited amount of fuel inside the reactor at any time. The ITER fuel is a gaseous mixture, a plasma of deuterium and tritium. In order to maintain the fusion reaction we rely on the continuous supply of fuel. If the fuel supply is interrupted for any reason, the fusion process stops immediately. There is absolutely no danger of a nuclear meltdown or a runaway reaction.

Moreover, loss of the cooling function due to an earthquake would not affect the confinement barrier at all. Even in the case of the total failure of the water cooling system, ITER's confinement barriers will remain intact. The temperatures of the vacuum vessel that provides the confinement barrier would under no circumstances reach the melting temperatures of the materials.

What about the issue of nuclear decay heat that was so serious at Fukushima?

It's true that continued cooling is required in a fission reactor because, even after shutdown, there is a substantial decay heat to be eliminated that is produced by the fission decay of the tons of nuclear fuel present in the vessel.

In ITER or in future fusion power plants, this kind of scenario is impossible. The thermal power induced in the ITER vacuum vessel will be low. Even if no active cooling of the vacuum vessel is provided, as in the case of total failure of the cooling system, the resulting temperature would not threaten the integrity of the vacuum vessel.

ITER will be built near a site with other nuclear installations. What is the additional risk due to the presence of more than one installation?

The safety analyses presented in the Preliminary Safety Report of ITER take the complete surroundings into account, including all installations, either nuclear or conventional, that could have an influence on ITER. These studies show that ITER safety will not be impacted by accidents occurring in surrounding installations.

What will be the total amount of tritium stored on site? What are the procedures foreseen to confine and control the stock?

The maximum amount of tritium in the facility will be set by the French safety authorities, and will not exceed 4 kg. The actual amount in ITER at any time will be determined by operational needs based on the ITER Research Plan.

Tritium will be stored as metal hydride (i.e., chemically bound to a metal) in dedicated vessels, called metal hydride beds. Metal hydride beds are very efficient for tritium collection and provide a safe way of storing tritium. Only the amounts necessary for operation of the fuel cycle will be liberated from the beds. Their confinement performance will follow a very strict qualification program; losses from the storage beds will only be due to the natural radioactive decay of tritium (half the tritium decays into inert helium every 12.3 years).

ITER has implemented not only state-of-the-art confinement methodologies but also above-and-beyond technologies to provide removal and recovery of tritium for the very unlikely event of tritium spilled into rooms. Control of stock is maintained is through a tritium tracking procedure and regular inventory measurements. Security measures will be in place to protect the tritium in stock.

What would be the effect on the population near ITER of potential accidental radioactive releases in the environment, including tritium?

The ITER design is such that, even if the containment were accidentally to be breached in the tokamak, the levels of radioactivity outside the ITER enclosure would still be very low. The ITER Preliminary Safety Report presents an analysis of risks and events that may cause accidents in the facility. During normal operation, ITER's radiological impact on the most exposed populations will be one thousand times less than natural background radiation and in "worst-case scenarios" such as fire in the tritium plant, evacuations or other countermeasures for the neighbouring populations would not be required.

What procedures are foreseen to avoid any loss of tritium, mostly during the first tests (incomplete fusion)?

Only a small fraction of the tritium in the tokamak is actually consumed during a plasma burn. Tritium will be separated from the exhaust gases pumped from the tokamak vessel, purified, and stored for reuse. The effectiveness of tritium removal from the room atmosphere and from the liquid effluents and recovery during tritium plasma operation is independent of the fusion performance of the tokamak. The design is based on a scenario in which no tritium is burned but it is all returned from the tokamak vessel to the recovery system.

Many provisions are implemented into the design to avoid losses of tritium. An efficient static confinement barrier will be installed in the areas where tritium is handled and air pressure cascading in the buildings will inhibit the outward diffusion of tritium. The static and dynamic confinement systems as well as radiological and environmental monitoring will be available for several years before tritium is put in the machine (i.e., from the beginning of the deuterium-deuterium phase of operation). Even the small amounts of tritium generated during deuterium-deuterium operation will be removed and eventually recovered through fuel cycle processing systems.

Can you declare fusion is really safe, while it uses huge amount of tritium, generates strong neutrons, and brings about huge amount of radiological waste?

It's true that the nuclear fusion reaction in a tokamak is inherently safe. Achieving fusion requires very precise conditions. If a plasma is too cold or too hot, if there is too much fuel or not enough, if there are contaminants in the plasma, or if the magnetic fields are not optimal ... the reaction dies out.

However fusion processes do involve radioactive materials. ITER, or the fusion power plants to follow, will have to manage the radiation produced through two mechanisms. One of the fusion fuels, tritium, is a radioactive form of hydrogen with a half-life of 12.3 years; the tritium absorbed by the infrastructure of the tokamak will give rise to some radioactivity. In addition, very fast neutrons produced by the fusion reaction will activate, over time, the material structures of the vessel.

The amount of tritium used during plasma pulses is very small—only a few grams at any one time. Careful procedures have been established for the handling and containment of tritium that have been well tried in other fusion facilities and through tritium applications in medicine and technology. An efficient static confinement barrier will be installed in the areas where tritium is handled and air pressure cascading in the buildings will inhibit the outward diffusion of tritium. Even if the containment were accidentally to be breached in the tokamak, the levels of radioactivity outside the ITER enclosure would still be very low. The ITER Preliminary Safety Report presents an analysis of risks that demonstrates that during normal operation, ITER's radiological impact on the most exposed populations will be one thousand times less than natural background radiation. Even in "worst-case scenarios," such as fire in the Tritium Plant, evacuations or other countermeasures for the neighbouring populations would not be required.

Fusion reactors, unlike fission reactors, would produce no high activity/long life radioactive waste. The "burnt" fuel in a fusion reactor is helium, an inert gas. Activation produced in the material surfaces by the fast neutrons will produce waste that is classified as very low, low, or medium activity waste. All waste materials will be treated, packaged, and stored on site. Because the half-life of most radioisotopes contained in this waste is lower than ten years, within 100 years the radioactivity of the materials will have diminished in such a significant way that the materials can be recycled for use in other fusion plants, for example. This timetable of 100 years could possibly be reduced for future devices through the continued development of "low activation" materials, which is an important part of fusion research and development today.

The activation or contamination of in-vessel components, the vacuum vessel, the fuel circuit, the cooling system, the maintenance equipment, or buildings will produce an estimated 30,000 tons of decommissioning waste that will be removed from the ITER facility and processed.

The ITER Organization was licensed as a nuclear operator in France in November 2012, following the in-depth technical inspection of its safety files. Because it is the first nuclear installation to be licensed in France since 2006, ITER is the first one to observe the 2006 French law on Nuclear Transparency and Security and the first fusion device in history to have its safety characteristics undergo the rigorous scrutiny of a Nuclear Regulator to obtain nuclear licensing.

Is there any possibility that fusion opens a new way for the production of mass destruction weapons?

There are no fissile materials like plutonium or highly enriched uranium in a fusion reactor that could be exploited to make nuclear weapons. The use of tritium in ITER will not open a new way for the production of mass destruction weapons. Tritium is already used commercially, in small quantities, for medical diagnostics and sign illumination.

At ITER, an integrated safety management system will be put into place to address all potential hazards in compliance with industrial safety regulations. Potential hazards will be addressed specifically by department, and appropriate safety measures put into place. Non-radiological hazards taken into consideration at ITER include fire, exposure to magnetic and electromagnetic fields, exposure to chemicals or cryogenic fluids, and high voltages. To protect workers, access to the Tokamak Building will be strictly forbidden during operation.

Physicists have been exploring the properties of plasmas within tokamak devices since the 1960s. It is well known that beyond certain operational boundary conditions—for example, when plasma current or pressure or density is raised too high for a given magnetic field—the plasma can become unstable.

A disruption is an instability that may develop within the tokamak plasma. Disruptions lead to the degradation or loss of the magnetic confinement of the plasma, and because of the high amount of energy contained within the plasma, the loss of confinement during a disruption can cause a significant thermal loading of in-vessel components together with high mechanical strains on the in-vessel components, the vacuum vessel and the coils in the tokamak.

In some cases, because of the large electric fields created during the disruptions, a relativistic electron beam (containing "runaway electrons") forms that can penetrate several millimetres into the in-vessel components when it is eventually lost from the plasma.

Unless mitigating action is taken, plasma-facing components can suffer local damage due to the thermal loads and to the deposition of runaway electrons during disruptions. In addition, in extreme cases, the mechanical strains on the components during disruptions may cause some deformation.

Disruptions are not triggered randomly; they only occur when well-defined limits are exceeded. Disruptions have been observed, avoided and mitigated in most operating tokamaks. One of ITER's objectives is to perfect a stable operating scenario through experimentation so that disruptions become a relatively rare event. During the first years of operation, ITER operators will most likely deliberately provoke disruptive events. Their aim will be to analyze, and to learn to control, these events at reduced plasma parameters and low plasma energy so that disruptions cannot cause damage to the ITER components in experiments at the highest plasma current and energy.

By "pushing" the machine toward disruptions at modest plasma parameters, ITER operators will find its stability boundaries. Once these stability limits have been identified, there is no reason for plasmas in the ITER Tokamak to become disruptive spontaneously as the plasma current and plasma energy is increased, provided that this is done within the stability region identified.

There is abundant literature on the subject of disruptions (see, in particular, Nuclear Fusion) and on the operational strategies to avoid disruptions and to mitigate their effects when they cannot be avoided.

Disruptions are an integral part of the official (and public) physics basis for ITER, which has been extensively refereed by the scientific community ("ITER Physics Basis," Nuclear Fusion, 47; 2007 complemented the initial 1999 report). Disruptions represent an active field of research in the fusion community in order to perfect the avoidance and mitigation schemes being developed for ITER.

The European tokamak JET and the French tokamak Tore Supra, as well as many others in the world, have been operated in a completely safe and satisfactory manner since 1983 and 1988 respectively. When exploring new plasma regimes, or during dedicated experiments to study disruptions and their mitigation, disruptions can occur several times a day in these two machines and others, but they have never led to the destruction or rupture of their vacuum vessels.

Because disruptions are expected in ITER, they have been planned for. The ITER vacuum vessel and in-vessel components have been designed to withstand the forces produced by about 3,000 disruptions at full plasma performance over the course of their lifetime. ITER's resistance to disruptions is based on scaling laws ("engineering laws") that have determined the values chosen for ITER; these values have been validated by experiments on other tokamaks.

It is important to understand that disruptions are not a safety-class issue for ITER: there is absolutely no risk for the integrity of the vacuum vessel. But as the high energy loads during disruptions can, over time, damage the surface of plasma-facing components such as divertor targets and first wall panels, these components may need—and have been designed—to be replaced. This takes time and reduces the availability of ITER for experiments. It is therefore important to develop disruption mitigation techniques that reduce the forces and the energy loads on ITER's components so that the time between interventions to replace these components is as long as possible, thereby optimizing the scientific exploitation of ITER.

During the progressive commissioning of ITER, the machine will be tested with plasma currents and plasma energies lower than the nominal values required for fusion energy production. In this way, the potential degradation of ITER's components by disruptions during this initial learning phase will be minimized. We will begin with low current and low-energy plasmas to learn how to avoid and mitigate the effects of disruptions on ITER before moving on to more advanced operational scenarios with higher currents and higher energies (thus larger forces and energy loads on components).

The ITER strategy is not radically different from that already followed in the operation of the largest existing tokamak JET, which achieved plasma currents of 6-7 MA (as compared to the 15 MA nominal plasma current planned in ITER).

In summary, the ITER engineering design allows for disruptions to occur in approximately 10 percent of plasma pulses. The early, low-energy/low-plasma-current phase of ITER will permit physicists to characterize disruptions on ITER without risks to the machine. Disruption mitigation is one of the specific scientific missions of ITER, with direct relevance to the future development of fusion power plants based on the tokamak concept.

ITER's Disruption Mitigation System (DMS) is currently in its design phase. In determining the best method, or combination of methods, for disruption mitigation, the ITER Organization is taking into account performance, reliability, flexibility, and cost.

Two promising methods are on the table that will be further refined in the coming months and years for ITER scenarios. Following years of development work, shattered pellet injection—in which massive amounts (up to 500 g) of particles are introduced into the plasma within 10 milliseconds—has been chosen as the baseline technique to disperse the energy of a disruption before it can concentrate its load on the wall of the containment vessel. Develpment work on a second approach, massive gas injection, will continue as part of risk mitigation.

An R&D program in disruption mitigation for ITER is currently underway. Experiments run on the ASDEX Upgrade (Germany), Tore Supra (France), DIII-D (US), and JET (EU), to cite a few of the tokamaks involved in this research, are contributing to the refinement of predictions for disruption mitigation in ITER. The ever-increasing capability for numerical simulation of disruptions is also being applied in the elaboration of the ITER disruption mitigation strategy.

The Disruption Mitigation System in ITER will function automatically, triggered as disruptions occur during plasma pulses by dedicated sensors and algorithms that can evaluate the likelihood of an impending disruption. With at least 10 pulses planned per day during operational phases, and disruptions expected in approximately 10 percent of these, it is accurate to say that the Disruption Mitigation System will operate routinely—probably daily—during operation, at least during the initial phases as the ITER operational scenarios are being developed.

Why has fusion science developed much more slowly than fission science, which provided commercial reactors just a few years after its inception?

The main answer to this question comes from the nature of these two sciences and their technological applications. In terms of complexity (in both science and technology), there is more than one order of magnitude of difference between fusion and fission.

The core science of fusion is plasma physics, which is highly complex due to its non-linear and stochastic processes. The mastery of the physics is not yet sufficient to enable the construction of a fusion power plant, which requires cutting-edge technologies like superconductivity, high vacuum, and cryogenics. An important mission of ITER is to prove once and for all that it is possible to integrate all these technologies into a single device. The technologies for fission, on the other hand, have evolved over generations of fission machines.

Will commercial fusion be available early enough to contribute to the energy transition needed to fight climate change and to replace fossil fuels?

The next decades are crucially important to putting the world on a path towards much reduced greenhouse gas emissions. Current and near-term technologies should be deployed as soon as possible for this purpose. However world population will continue to grow and the proportion of populations living in cities is expected to continue to increase. Together with the need for a more equitable distribution of energy among the world's inhabitants, this means that even more large-scale, low-CO₂ sustainable energy will be needed later in the century. Fusion is a strong candidate.

Fusion is one of the few potential alternatives for large-scale energy production. ITER is a major step in this direction that will demonstrate the physics and technology on the way to fusion power plants. Achieving success in ITER will not lead immediately to the building of fusion power plants; another step, usually called DEMO (DEMOnstration fusion power plant) will be necessary. Building on the knowledge and know-how acquired within ITER and parallel research, DEMO will mark the transition to the deployment of fusion energy systems.

The timescale to commercial fusion therefore extends until at least the middle of this century, depending strongly on the political will to invest in this area of research. Lev Artsimovitch, the famous Russian academician and one of the major figures in fusion history, used to say: "Fusion will be ready when society needs it."

If successful, when would fusion be able to add power to the grid? What steps would be required after ITER?

ITER is the essential bridge between today's smaller-scale experimental fusion devices and the demonstration fusion power plants of the future. ITER is a scientific experiment that will open the way to industrial and commercial production of fusion energy.

Building on the knowledge and know-how acquired within ITER, as well as research carried out in parallel on other fusion devices, the next-step machine—an industrial demonstrator (DEMO)—would demonstrate the large-scale production of electrical power and tritium fuel self-sufficiency. Several conceptual designs for such a machine are already on the table in the ITER Members; these designs will be refined as ITER enters operations.

In 2012 the European Fusion Development Agreement EFDA, which reunites European fusion R&D laboratories, published A Roadmap to the Realisation of Fusion Energy that outlines its plan for bringing fusion electricity to the grid by 2050—a goal that it considers ambitious, yet realistic. It foresees a DEMO that will produce net electricity at the level of a few hundred megawatts in the early 2040s. The EFDA Roadmap takes into account R&D currently undertaken by Europe and Japan within the framework of the Broader Approach activities.

Japan, Korea, India and Russia have also stated their intention to begin building DEMO in the early 2030s in order to operate it in the 2040s.

China plans to first explore physics and technological issues in a test reactor built in the 2020s (the China Fusion Engineering Test Reactor, CFETR) before launching the construction of DEMO in the 2030s.

Of course there are likely to be political and economic constraints that we cannot foresee. The final timescale to commercial fusion depends strongly on political and private sector will to invest in this area of research.

How much power would a fusion reactor be able to deliver and at what cost? Would it be competitive?

The power output of the kind of fusion power reactor that is envisaged for the second half of this century will be similar to that of a fission reactor, i.e., between 1 and 3 gigawatts. In theory, the larger the reactor, the more efficient it would be to operate and the more power it would produce, so it may be advantageous to go larger in the future. For the moment, it is envisaged that future fusion power plants would occupy buildings no bigger than those that presently house fission or coal-fired power stations.

The main goal of ITER and future fusion reactor-based power plants is to develop a new, sustainable and virtually unlimited energy source. The average cost per kilowatt of electricity is expected to be similar to that of current fission reactors ... slightly more expensive at the beginning, when the technology is new, and less expensive as economies of scale bring the costs down.

In order to have a rapid market penetration, fusion will have to demonstrate the potential for competitive cost of electricity. Although this is not a primary goal for DEMO, the perspective of competitively priced electricity production from fusion has to be set as a target. One way to do this is to minimize DEMO capital costs (and that of fusion power plants). The ITER Tokamak is a first-of-a-kind experimental machine, built with a vast array of diagnostic systems (over 40!) to learn as much as possible about what is happening in the plasma. A fusion power plant on the other hand would be conceived in quite a different way.

Is there any assurance that there will be enough tritium available for commercial deployment of fusion? Are lithium resources sufficient to fuel future fusion reactors in competition with other lithium usages?

All the conceptual power plant studies performed in the European fusion program have shown that the commercial deployment of fusion would not be limited by the availability of fuels and raw materials. Deuterium fuel and lithium (the raw material for tritium fuel, which is produced by fusion neutrons interacting with lithium), are both widely distributed on Earth:

deuterium is a naturally occurring isotope of hydrogen, available in water and easily extracted from it;

lithium from proven, easily extractable land-based resources would provide a stock sufficient to operate fusion power plants for more than 1,000 years (each fusion plant would need only about 3 tonnes of lithium per year). Worldwide resources of lithium are presently estimated at 25 million tonnes and studies have shown that competition with other uses, such as batteries, will not be an issue. What's more, lithium can be extracted from ocean water, where reserves are practically unlimited (enough to fulfill the world's energy needs for ~ 6 million years).

Is the concept of tritium breeding sufficiently robust to start the ITER Project?

Future fusion power plants will have to produce tritium; however, tritium self-sufficiency is not necessary in ITER. Rather, one of the missions for the later stages of ITER operation is to demonstrate the feasibility of one or more concepts of tritium production through the Test Blanket Module (TBM) program. The TBM program will build on tritium breeding studies that have been carried out for a number of years, in particular by the European Union which has substantial expertise in this field. The accumulated knowledge permits a high level of confidence that results from ITER will contribute to full tritium self-sufficiency in next-generation devices.

I recently read that there was a shortage of helium in the world and this was unlikely to improve as stocks are used up. How will this affect plans for the fusion superconducting magnets?

ITER and future fusion machines based on present superconductor technology would require only a fraction of the present total world helium production.

One of the major helium reserves is the US strategic helium storage reserve; this was released for sale and quantities will reduce in the coming years but will be compensated with new helium sources going into production around the world at the same time. There are also several other untapped helium reserves that ensure sufficient production for party balloons and MRI magnets (some of the main users of helium).

While it is uncertain what the price of helium will be in the coming decades (it will depend on supply and demand), there shouldn't be any significant shortage for fusion.

In the future, fusion machines will have the capability to breed not only their own fuel (tritium) but also helium to preserve natural reserves.

What are the benefits of pursuing fusion as compared to next-generation nuclear fission reactors?

Fusion and fission are totally different scientific and technological concepts, although both involve nuclear reactions. The fuel assemblies in the core of a fission reactor contain several tons of radioactive fuel which generates energy by the splitting ("fissioning") of atomic nuclei in a chain reaction. Fusion is not a chain reaction. The entire system contains a few kilograms of the radioactive fuel component (tritium) with only a few grams reacting at any given time in the reaction chamber.

Three very unique safety features make fusion technology an attractive option to pursue for future large-scale electricity production.

First, fusion presents no risk of nuclear proliferation. Unlike the fissile materials such as uranium and plutonium used in fission reactors, tritium is neither a fissile nor a fissionable material. There are no enriched materials in a fusion reactor like ITER that could be exploited to make nuclear weapons.

Second, nuclear fusion reactors would produce no high activity/long-life nuclear waste. The "burnt" fuel is helium, a non-radioactive gas. Radioactive substances in the system are the fuel (tritium) and materials activated while the machine is running. The goal of the ongoing R&D program is for fusion reactor material to be recyclable in less than 100 years.

Third, fusion reactions are intrinsically safe. A "runaway" reaction and the resulting uncontrolled production of energy is impossible with fusion. Fusion reactions cannot be maintained spontaneously: any disturbance or failure stops the reaction. This is why it is said that fusion has inherent safety aspects. Moreover, the loss of the cooling function due to an earthquake or flood would not affect the confinement barrier at all. Even in the case of the total failure of the water cooling system, ITER's confinement barriers will remain intact. The temperatures of the vacuum vessel that provides the confinement barrier would under no circumstances reach the melting temperatures of the materials.

Nuclear risks associated with fusion relate to the use of tritium, which is a radioactive form (isotope) of hydrogen. However, the amount used is limited to a few grams of tritium for the reaction and a few kilograms on site. During operation, the radiological impact of the use of tritium on the most exposed population is much smaller than that due to natural background radiation. For ITER, no accident scenario has been identified that would imply the need to take countermeasures to protect the surrounding population.

Is it really possible to find materials which can cope with strong fusion neutrons?

Along the road to the successful development of fusion, one of the major challenges will be to develop materials that can maintain their essential physical properties and not remain highly radioactive for extended periods of time after exposure to the harsh thermal and irradiation conditions inside a fusion reactor.

Fusion R&D has already successfully developed reduced-activation steels. Further developments are foreseen for steel as well as for other materials with more advanced features for fusion reactor applications.

EURATOM and Japan signed a Broader Approach agreement in 2007 that aims to complement the ITER Project by carrying out R&D and developing some advanced technologies for future demonstration fusion power reactors (DEMO). Work is currently underway to complete the integrated engineering design of the International Fusion Materials Irradiation Facility (IFMIF) which will test and qualify advanced materials in an environment similar to that of a future fusion power plant.

How often will the ITER first wall need to be replaced during operation?

The current operation schedule does not include the replacement of the ITER first wall. However, provisions have been made for the possibility of changing it once during the lifetime of ITER, if necessary. The component which receives most of the power load from the plasma (the "divertor") will need to be replaced more than once during the lifetime of the machine. It has been designed specifically to allow this operation by remote handling. Individual components may also need to be replaced from time to time for corrective maintenance.

What are the procedures to dispose of the irradiated material contained in the first wall? Have safety risks been taken into account?

The irradiated material will be transferred within a confinement cask to enclosed, shielded compartments ("hot cells"). Inside the hot cells, several operations will be performed such as cleaning and dust collection, detritiation, refurbishment, and disposal. The waste, which is classified as medium level, will be stored in the hot cells. All of these procedures are a part of ITER operation as presented in the Preliminary Safety Report, and consequently are also submitted to examination of the French Nuclear Safety Authority.

Remote handling technologies have been developed for fusion applications, for example they have been extensively used in the recent upgrade of the Joint European Torus (JET) facility to ensure that workers are not exposed to radioactive components.

Is there any risk of damage in case of loss of superconductivity in the ITER superconducting magnets?

The fusion science community has an experience of more than twenty years operating large superconducting magnets, i.e., Large Helical Device (Japan), Tore-Supra (France).

Any loss of superconductivity is easily detected, and safety circuits place external resistors in series with the coils to absorb the stored energy. If the safety system and its backups were to fail the coils might suffer damage, but there is no possibility of threat to the integrity of the first confinement barrier.